ES2939347T3 - Gas injection element, oven equipped with such an element and its use - Google Patents

Abstract

The invention relates to a gas injection element having a heat-tensile tubular wall (3) and having a proximal end and a distal end (11), at this distal end, at least one end opening through which at least one gas is sprayed, and a cooling system is housed in the tubular wall comprising axial channels (12) that extend axially towards the distal end and in which a cooling fluid is circulated, and connection channels (13) connecting the axial channels circumferentially to the distal end of the tubular wall, the connecting channels, circumferentially connecting the axial channels to the distal end of the tubular wall, presenting a rounded shape in the direction of this distal end. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Gas injection element, oven equipped with such an element and its use

The present invention refers to a gas injection element, comprising:

- a tubular wall capable of being subjected to thermal stress, and having a proximal end and a distal end,

- at this distal end, at least one end opening through which at least one gas is expelled, and

- a cooling system that is housed in said tubular wall, and comprises axial channels that, between a proximal end and a distal end, extend axially towards said distal end of the tubular wall, and in which a fluid is circulated connection channels circumferentially connecting the aforementioned axial channels to each other at their distal termination, these connection channels presenting a rounded shape in the direction of the distal end of the tubular wall.

Such gas injection elements are used, in particular, in the electric segment of steel production, more particularly, in an electric furnace. In an electric arc furnace, each manufacturing cycle, called "casting", comprises four stages, loading the scrap, melting it, refining the molten steel, and pouring it out of the furnace.

The melting stage is mainly affected by the input of heat, in the most efficient way possible, with a view to accelerating the melting of the solid scrap. To do this, it takes energy from 3 inputs: the electric arcs developed in the furnace, the flames coming from burners placed on the walls of the furnace, and the iron decarburization and oxidation reactions.

The refining stage gives priority to a chemical oxidation reaction of carbon and other chemical elements, through the oxygen supplied. The refining extracts its chemical energy from the expulsion of oxygen at supersonic speed into the bath of molten metal.

Various accessories are needed depending on the specifics of each steel mill's process, accessories that, for the most part, are fixed to the side walls of the furnace and blow at an angle towards the bath. Among these accessories are the burners, which expel a combustible gas and oxygen as an oxidizer, so that a flame is formed. Combination burners are also envisioned, which can not only produce a flame, but can also expel supersonic oxygen into the bath.

Burners, or combination burners, are essential elements of productivity and quality of electric arc furnace steelmaking.

As a heat input element, and as an expulsion element of the refining reaction motor, that is to say oxygen, the burner must be dimensioned, in a dedicated manner, to the method implemented and to the converter.

The problem consists both in guaranteeing the characteristics and qualities of the burners and in preserving them over time throughout a campaign of thousands of pours, in order to perpetuate the different performances of the converter.

Indeed, throughout the thermomechanical cycles induced by the succession of castings, the burner wears out due to erosion and cracking, due to numerous and varied stresses. The thermal stresses are due to the radiation from the bath, to the flame, to the atmosphere, to the return of flame by rebound on the scrap, to the proximity of the electric arc and to the coating by hot foaming slag. Mechanical stresses may also appear, such as expansion and retraction cycles, scrap impact, arc discharges.

To withstand these stresses, the burner must be cooled by a cooling fluid. The most highly stressed areas are, in general, the front part of the burner, which faces the interior of the furnace, that is, its distal end, and the interior of the burner, or its mixing chamber, exposed to the flame of the burner. Attempts to solve these problems are already known.

Mention may be made, for example, of burner cooling systems in which a cooling fluid circulates in coaxial channels arranged peripherally on the external wall of the injector (see documents WO2007/100441 and US-2010/0252968). A cold cooling fluid is injected into the central channel of one of these coaxial channels, towards the distal end of the injector. At that moment, after the heat exchange, it is returned through the coaxial channel that surrounds the central channel, having to make a sudden 180° change of direction. As a result of this arrangement, at the distal end of the coaxial channels, that is, in the place where the cooling must present the greatest performance, the formation of foaming occurs. of the cooling fluid, usually water. This foamed fluid is thermally insulating and should be avoided. In addition, through the coaxial arrangement of the channels, the hot fluid from the coaxial return channel performs a thermal exchange with the fluid that runs through the central channel, before it reaches the area with the greatest thermal demand, which, obviously, also it is undesirable.

A burner cooling casing formed by several longitudinal segments arranged side by side is also known (see US Pat. No. 5,176,875 and DE202007019294 U1). Two channels in which a cooling fluid circulates extend axially in each segment of this casing. These two axial channels are connected by means of a transversal channel, perforated perpendicular to them. The cooling fluid enters through one of the axial channels and exits through the other, undergoing a sudden change of direction of displacement, with formation, also in this case, of a thermally insulating foam. The other drawback of this assembly lies in the fact that the multiple contact surfaces between longitudinal segments placed one next to the other represent as many obstacles to the uniform propagation of heat inside the casing, reducing its cooling efficiency.

A burner is also known in which the cooling channels end in a cooling die made inside the nozzle, the assembly being manufactured by means of a 3D printing system (see document DE 102016 211 477 A1). A burner, according to this previous document, requires a significant amount of time to be completed, in fact, only one part can be printed in 3D before the next, which is not foreseeable from an industrial point of view. In addition, heat transfers are heavily penalized due to the lack of compactness of the material and the lower metallurgical quality. Furthermore, the surface condition of the burner, according to this document, cannot be controlled well.

Finally, some devices have tubular casings formed by two sleeves that fit one into the other, and that are shaped in such a way that they form axial grooves with each other that can communicate, eventually, in a rounded manner (see documents JP 2015 161460 A and WO 2011 /044676). Again, these devices have large, mechanically brittle and thermally insulating joint surfaces.

The purpose of the present invention is to solve the problems presented by the gas injection elements according to the prior art and, in particular, to increase their useful life, while simultaneously guaranteeing a high heat transfer for any flow rate of cooling fluid.

For this purpose, according to the invention, a gas injection element is provided, as described in the preamble of this description, and in which the tubular wall is one-piece, said axial channels axially traversing this one-piece tubular wall, which has , at the distal end of the axial channels, a circumferential groove, the injection element also comprising a closing crown, which seals said circumferential groove of the monobloc tubular wall, said round-shaped connection channels being arranged between said groove circumferential and said closing crown.

Advantageously, said closure ring can be formed by at least two ring elements.

By monobloc tubular wall, it is to be understood that the slotted tubular wall of the injection element according to the invention is in one piece. The crown intended to close the slot in the tubular wall is therefore enclosed in the body of a single piece of the tubular wall in one piece.

When the slot is closed by the closing crown, there is metallic continuity between it and the rest of the tubular wall.

By means of the compact casing, formed by the monobloc tubular wall, a continuity of heat conduction is obtained, without thermal resistance coming from contact surfaces, for example, held by clamps. Therefore, the temperature distribution is more homogeneous, and the heat flow is more important. The highly conductive material that forms the monobloc wall, such as high purity copper, for example, allows a large amount of heat to be rapidly transferred from the hot source (the monobloc wall) to the cold source (the integrated water circuit). This results in a high heat transfer to the fluid circuit and therefore a lower and more uniform temperature of the monobloc wall material. Therefore, its erosion is slowed down, which increases its useful life.

In addition, the monobloc tubular wall according to the invention advantageously makes it possible to substantially reduce the phenomenon of cracking that generally occurs at the joining surfaces of the different components at the end of the gas injection element. According to the invention, the axial channels, for example perforated longitudinally in the tubular wall, require, in order to communicate with each other, the undercutting of a circumferential slot with a low surface area and then the closure of this slot by means of a crown. The joining surface between the groove and the crown is low, it is located on the periphery of the monobloc tubular wall, and it is framed by its solid material. The thermal stresses, after the expansion of the body, are mainly radial. Therefore, they are in the joint plane, while it is mainly the stresses perpendicular to the joint plane that can cause cracking. Finally, since the joints are framed by the solid material of the monobloc tubular wall, they therefore benefit from additional reinforcement.

On the other hand, in order to guarantee efficient cooling of the tubular wall throughout the entire path of the cooling fluid, it is essential to avoid the phenomenon of foaming of the cooling fluid, the foam formed being thermally insulating. This foaming occurs during the presence of shape accidents in the path of the cooling fluid. Due to their rounded shape, oriented towards the distal end of the tubular wall, the connection channels of the cooling system according to the invention avoid sudden changes in the direction of movement, and also limit pressure losses and instabilities. By rounded shape is to be understood, according to the invention, a smooth transition between the ends of two axial channels. This shape makes it possible to avoid having to contour marked or sharp edges. It can easily be obtained by forming the bottom of the circumferential groove, of the crown elements that serve to close the groove, or simultaneously of all these components.

The distal end of the tubular wall is to be understood, according to the invention, as the end of the tubular wall of the gas injection element, which is opposite its fixing end in an oven or a burner, for example, called end proximal.

By axial channels, channels are to be understood which extend parallel to the axis of the tubular wall.

Advantageously, said connection channels have the shape of an arc of a circle, of an ellipse or of a parabola. However, these shapes are not limiting.

This particular rounded shape of the connection channels allows a stable conduction of the fluid, which allows high flow velocities and, therefore, high Reynolds numbers, without, therefore, encountering and increasing head losses and instabilities, as described causes in the presence of accidents of form. In this way, it is possible to put into practice a turbulent flow regime, that is to say, with a high Reynolds number, obtained for a high velocity of the fluid that runs through the circuit. This type of flow favors intense thermal exchanges inside the fluid, and prevents any excessive thickening of the kinetic and thermal boundary layers at the metal/fluid interface. This guarantees a high thermal gradient between the cold fluid and the hot metal, favoring the extraction of heat out of it. This also prevents the creation of a layer of foaming water, which is insulating, in contact with the tubular wall, which appears in the event of an increase in temperature.

According to a particular embodiment of the invention, the gas injection element forms a burner injector provided with said one-piece tubular wall, in which said cooling system is housed. This is the case in particular for burners that give rise to the formation of a flame, which are used, for example, during the melting of scrap.

According to another form of the invention, the gas injection element forms a casing provided with said one-piece tubular wall, in which said cooling system is housed. It is common for the end of a burner to be covered, at least partially, by a sleeve. This may be a separate element from the burner, which may be fitted at the injector end.

According to yet another embodiment of the invention, said sheath is arranged at one end of a burner injector, covering it, at least partially. Therefore, the gas injection element then forms a burner-sheath assembly, which can be a monobloc element.

Protruding at the end of the injector, the sheath forms a mixing chamber, where, for example, gas mixing can take place leading to a flame, but also where supersonic oxygen can be expelled, representing a combi burner. .

According to one form of the invention, passageways further connect axial channels circumferentially at their proximal end.

These passage channels can also have a rounded shape, but in the opposite direction to the distal end of the tubular wall.

Advantageously, the one-piece tubular wall has, at said proximal end of the axial channels, an additional circumferential groove, the injection element also comprising an additional closing crown, formed by at least two crown elements, which seals the circumferential groove. of the monobloc tubular wall, said passage channels being arranged between said additional circumferential groove and said at least two elements of the additional closing crown.

According to another embodiment of the invention, the monobloc tubular wall is presented, between said proximal termination of the axial channels and the proximal end of the tubular wall, in the form of a thinner connector, also comprising the injection element, a flange that is embedded in the connector of the monobloc tubular wall, said passage channels being arranged between said connector and said flange.

These passage channels can easily be obtained by forming the bottom of the additional circumferential groove, of the crown elements that serve to close the additional groove, or simultaneously of all these components. In the case of fitting a flange into a connector of the monobloc tubular wall, the passage channels can be formed in the connector, in the flange or in both elements simultaneously.

According to an improved embodiment of the invention, the cooling system is made up of at least one cooling coil, comprising several axial channels arranged in parallel in succession in the tubular wall, and successively connected to each other by a connection channel, then through a through channel, then again through a connecting channel, and so on. Advantageously, each cooling coil comprises, for the cooling fluid, an inlet and an outlet arranged in the tubular wall, at a distance from the distal end thereof. In particular, the cooling system comprises two cooling coils each covering one half of the tubular wall of the gas injection element.

According to a particular form of the invention, said distal end of the tubular wall has a part that is most intensely subjected to thermal stress, and the axial channel(s) fed directly by said inlet of cooling fluid, open up in this part that is most intensely subjected to thermal stress. thermal.

In this way, the cold inlet cooling fluid is directed directly to the most appropriate areas, which must be more protected, while the cooling fluid that has already been heated by heat exchange circulates, before leaving, in the axial channels arranged in the part less intensely subjected to thermal stress of the tubular wall.

Advantageously, the axial channels, the connection channels and the passage channels have a constant flow section. This constant section of the channels avoids disturbing variations of the flow.

Preferably, said at least one expelled gas is chosen from the group consisting of oxygen, supersonic oxygen, air, carbonated gases, nitrogen, and their mixtures, these gases being able to appear in the form of a flame, after combustion. Advantageously, the tubular wall is made of copper or a copper alloy.

The present invention also relates to a furnace provided with at least one gas injection element according to the invention.

The invention also refers to the use of at least one gas injection element according to the invention, for the treatment of a metallic material in a furnace, specifically, for the melting of scrap, the refining of steel in an electric furnace, or the slab heating.

Other details and particularities of the invention will emerge from the description given below, by way of non-limitation, of an example of embodiment of the gas injection element according to the invention, illustrated in the attached drawings.

Figure 1 represents a profile view of a gas injection element according to the invention.

Figure 2 represents a cross-sectional view, along the line II-II, of the gas injection element of Figure 1, on an enlarged scale.

Figure 3 represents a cross-sectional view, along the line III-III, of the gas injection element of Figure 1, on an enlarged scale.

Figure 4 represents a cross-sectional view, according to line IV-IV, of the gas injection element of Figure 1, on an enlarged scale and exploded.

Figure 5 represents a front view of the end of the gas injection element, according to Figure 1, on an enlarged scale.

Figure 6 represents a sectional view, according to the line VI-VI of Figure 5.

The gas injection element, illustrated in the figures, is a burner provided with a sheath. It comprises a tubular injector 1 whose end opening is partially covered by a sheath, generally designated by the reference 2. This has a one-piece tubular wall 3, which forms, around the injector, a casing which, as illustrated in the figures, it is cooled by a cooling system.

In Figure 1, the vertical wall of the furnace, on which the burner is arranged in an inclined manner, is schematically illustrated by the dashed line 4.

The burner injector is fed with fuel, for example natural gas, through inlet 5, and with oxidizer, for example, technical oxygen, through inlet 9. During operation, a flame is formed in the enclosed mixing chamber. through the tubular wall 3, and exits through an opening 10 provided in the distal end 11 thereof. In addition, if necessary, supersonic oxygen can be fed into the injector 1, through the supply conduit 6.

In the example illustrated in these figures, the cooling system of the casing 2 comprises a supply conduit 7 for a cooling fluid, and a conduit 8 for evacuation thereof.

As can be seen from Figures 2, 4 and 6, the cooling system comprises several axial channels 12 which extend axially towards the distal end 11 of the tubular wall. In these channels circulates the cooling fluid, for example, water, which comes from the supply conduit 7, and is directed, then, towards the evacuation conduit 8. These channels are perforated in the body of the monobloc tubular wall.

Circumferentially adjoining axial channels are connected, at the distal end 11 of the tubular wall 3, by connecting channels 13 having a rounded shape, in the direction of this end. In the example illustrated in Figure 6, the connecting channels 13 have a rounded shape, and therefore guarantee a smooth transition between the axial channels connecting them.

At a distance from the distal end 11 of the tubular wall, i.e. closer to the furnace wall, circumferentially adjoining axial channels are connected by passage channels 14, which have a slightly rounded shape, in the opposite direction to the aforementioned distal end 11 .

In the illustrated example, the axial channels 12 arranged in succession on the periphery of the tubular wall 3 are successively connected to each other, by a rounded connection channel 13, then by a rounded through channel 14, then again by a channel 13 rounded connecting piece, and so on, so that at least one cooling coil is formed in the tubular wall 3. The communication between the axial channels is carried out individually, gradually, without the need for coaxial channels that generate foaming, or confluences between several channels.

In the illustrated example, in particular, with reference to Figures 3 and 6, it can be seen that the supply conduit 7 for the cooling fluid opens in front of the inlet 15 of two axial channels 12, so that they are thus fed mode, two cooling coils each covering one half of the tubular wall 3. In Figure 5, the arrow indicates the location of the supply conduit 7 behind the tubular wall. The two outlets 16 of these coils end in a peripheral channel 17 that ends in front of the evacuation conduit 8 for the cooling fluid. The channels thus form two cooling circuits, distributed in differentiated circumferential zones inside the tubular wall. These circuits are fed by the same fluid source, conduit 7, and end in the same discharge, conduit 8.

As can be seen in particular from FIGS. 1, 4 and 6, the tubular wall is one-piece and has, in the illustrated embodiment, a circumferential groove 19 at the distal end of the axial channels 12. This groove is sealed by a closing crown formed, in the illustrated example, by two half crowns 20 and 21. The connecting channels 13 are formed, in the illustrated example, on the one hand in the bottom of the circumferential groove 19, and , on the other hand, inside the half-crowns 20 and 21. Obviously, their arrangement can also be provided solely at the bottom of the groove, or only inside the half-crowns.

This monobloc arrangement at the end of the gas injection element according to the invention, in the part most subjected to mechanical and thermal stress, makes it possible to minimize the rupture of metallic continuity, and thus produce an excellent capacity for balanced temperature field in the metallic alloy used, with a rapid transfer of calories from the heat source to the cooling liquid. By incorporating the half-crowns 20 and 21 radially in the circumferential groove 19, i.e. in the solid material of the monobloc tubular wall 3, a highly crack-resistant arrangement is obtained, which simultaneously allows an optimized flow of the fluid in the cooling system.

During operation of the furnace, the distal end 11 of the tubular wall 3 is particularly subjected to thermal stress, not only by the heat sources coming from the furnace, for example, the molten metal bath or electric arcs, but also by the flame present in the burner nozzle cavity. Due to the inclined arrangement of the burner on the refractory wall of the furnace, a part of the distal end of the tubular wall 3 of the sleeve protrudes further into the furnace and is therefore more particularly subjected to thermal stress.

In the illustrated example, the feed conduit 7 for the cooling fluid is arranged so that two axial channels 12 arranged in this protruding part of the tubular wall 3 are directly fed. In this way, the two axial channels 12 each open directly into the part subjected to the most thermal stress of the distal end of the tubular wall. They form the beginning of two cooling coils, and allow the location of the incoming cooling fluid and, therefore, "cold" to the places most subject to solicitation.

As can be seen in particular from Figures 1, 3 and 6, at its proximal end, the monobloc tubular wall is in the form of a connector 22 of less thickness. A flange 18 is fitted to this connector. In the illustrated example, the passage channels 14, as well as the inlet 15 and the outlet 16 that lead to the supply ducts 7 and 8 for discharge, are formed, on the one hand, in the surface of the connector 22, and, on the other hand, inside the flange. Obviously, it can also be provided for its arrangement only on the flange 18, or only inside the connector 22.

An arrangement consisting of an additional groove 23, comparable to groove 19, and a crown formed by two or more crown elements, comparable to half crowns 20 and 21, may also be provided. The possible location of this additional groove is represented in mixed traces in Figure 1.

It is to be understood that the present invention is in no way limited to the embodiment described above, and that it may be modified within the context of the appended claims.

For example, a single cooling coil or three or more cooling coils may be provided.

By distributing a free number of cooling circuits, the section of the channels of which can be freely dimensioned, it is possible to adjust the velocity of the fluid for a very large range of flow rates of the cooling fluid and therefore a high Reynolds number, to which the thermal exchange coefficient is directly associated.

Claims (17)

Yo. Gas injection element, comprising: - a tubular wall (3) capable of being subjected to thermal stress, and which has a proximal end and a distal end (11), - at this distal end, at least one end opening (10) through which at least one gas is expelled, and - a cooling system that is housed in said tubular wall (3), and comprises axial channels (12) that, between a proximal end and a distal end, extend axially towards said distal end (11) of the tubular wall, and in which a cooling fluid is circulated, connection channels (13) that circumferentially connect the previously mentioned axial channels (12) to each other at their distal end, these connection channels presenting a rounded shape towards the distal end of the tubular wall, - the wall (3) being monobloc tubular, said axial channels (12) axially traversing this monobloc tubular wall, characterized in that the monobloc tubular wall presents, at the distal end of the axial canals, a circumferential groove; because the injection element also comprises a closing crown that seals the circumferential groove of the monobloc tubular wall; and because said rounded connection channels (13) are arranged between said circumferential groove and said closing crown. Gas injection element according to claim 1, characterized in that it forms a burner injector provided with said one-piece tubular wall in which said cooling system is housed. Gas injection element according to claim 1, characterized in that it forms a casing (2) provided with said one-piece tubular wall in which said cooling system is housed. Gas injection element according to claim 3, characterized in that said sheath (2) is arranged at one end of a burner injector (1), covering it, at least partially. Gas injection element according to one or other of claims 1 to 4, characterized in that the cooling system comprises passage channels (14) circumferentially connecting axial channels (12) at their proximal termination. Gas injection element according to claim 5, characterized in that the passage channels (14) that circumferentially connect axial channels (12) have a rounded shape in a direction opposite to the aforementioned distal end (11) of the tubular wall (3). Gas injection element according to one or other of claims 5 and 6, characterized in that the monobloc tubular wall (3) is presented between said proximal termination of the axial channels (12) and the proximal end of the wall ( 3) tubular, in the form of a connector (22) of less thickness; because the injection element also comprises a flange (18) fitted on said connector of the monobloc tubular wall; and because said passage channels (14) are arranged between said connector (22) and said flange (18). Gas injection element according to one or other of claims 5 and 6, characterized in that the one-piece tubular wall (3) has, at said proximal termination of the axial channels (12), an additional circumferential groove (23); in that the injection element also comprises an additional closure crown, preferably formed by at least two crown elements, which seals the additional circumferential groove of the monobloc tubular wall; and in that said passage channels (14) are arranged between said additional circumferential groove and said additional closing crown. Gas injection element according to one or other of claims 5 to 8, characterized in that the cooling system is made up of at least one cooling coil comprising several axial channels (12) arranged in parallel in succession, in the tubular wall (3), and connected to each other successively by a connection channel (13), then by a passage channel (14), then again by a connection channel (13), and so on. Gas injection element according to claim 9, characterized in that each cooling coil comprises, for the cooling fluid, an inlet (15) and an outlet (16) arranged on the tubular wall (3), at a distance from the distal end (11) thereof. Gas injection element according to any one of claims 5 to 10, characterized in that the axial channels (12), the connection channels (13) and the passage channels (14) have a substantially constant flow section. Gas injection element according to any one of claims 9 to 11, characterized in that the cooling system comprises two cooling coils each covering one half of the tubular wall of the injection element. 13. Gas injection element according to any one of claims 1 to 12, characterized in that said at least one expelled gas is selected from the group consisting of oxygen, supersonic oxygen, air, carbonated gases, nitrogen, and their mixtures, which may be these gases in the form of a flame, after combustion. Gas injection element according to any one of claims 1 to 13, characterized in that said closure ring comprises at least two ring elements. Oven provided with at least one gas injection element according to any one of claims 1 to 14. 16. Use of at least one gas injection element according to any one of claims 1 to 15, for the treatment of a metallic material in a furnace. Use according to claim 16, for melting scrap, refining steel in an electric furnace or heating slabs.